Iron ores are minerals and rocks that metallic iron can be removed from. Most of Earth's iron ore deposits are in sedimentary rocks. Chemical reactions combined iron and oxygen in ocean and fresh waters to produce these deposits over 1.8 billion years ago. Once organisms capable of photosynthesis began releasing oxygen into water, the oxygen combined with dissolved iron to make hematite or magnetite. These minerals fell to the sea floor forming banded sedimentary rocks.
A few of the most prevalent ores of iron and some of their properties include:
Hematite, or ferric oxide, Fe2O3, - color is steel, silvery gray, or black with metallic luster. Hardness is between 5.0-6.0. Specific gravity is 5.3.
Magnetite, or iron oxide, Fe3O4, - color is black with submetallic luster. Hardness is 5.5-6.5.
Limonite, or ferric oxide, Fe2O3, - color medium to dark yellow brown with dull to earthy luster. Hardness is 1.0-5.0. Specific gravity ranges from 2.7 - 4.3
Iron ore is mined to make iron and steel products we use everyday from paperclips to cars!
The above answer is correct but I would like to add the following:
1. Ores are different than minerals in a way that ores contain the active ingredient, in this case an oxide of iron, in a quantity which can be used to extract the metal commercially. It means that it has lowe propotion of impurities.
2. Magnetite is Ferrouso-Ferric Oxide (FeO+Fe2O3) and has natural magnetic properties.
3. Limonite is Hydrous Iron Oxide FeO(OH)
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